1. Field of the Invention
This invention relates to a mechanism that connects a boom swing-house of a forestry machine to the frame of the ground engaging carriage of the machine, and more particularly to such a mechanism which is operated so as to level the swing-house in uneven or sloping terrain.
2. Discussion of the Prior Art
Forestry machines, such as feller bunchers for harvesting standing trees, are well known. In one type of feller buncher, a saw head which is used to sever the tree is mounted at the end of a boom which has its other end mounted to a turntable so as to be pivotable about a lateral axis relative to the turntable. The turntable is mounted to a turntable support so as to be pivotable about a vertical axis (when the support is vertical). A carriage which can have tracks or wheels for conveying the turntable support has a frame to which the turntable support is mounted by a leveling mechanism. The leveling mechanism is operable to vary the position and orientation of the turntable support relative to the carriage, depending upon the slope of the terrain and the orientation of the carriage on the terrain. For example, if trees are being cut on a hillside, the machine will typically be driven onto the hillside so the trees are within reach of the boom and the leveling mechanism adjusted so as to make the axis of the turntable generally vertical. The center of gravity of the swing-house assembly, which includes the boom (with cutting head attached), the engine of the machine and the operator cab, which are mounted on the turntable, should be positioned relative to the carriage so that the machine does not tip forward or backward when the tree is cut and its weight comes to rest on the butt plate of the head.
Such a mechanism may be made using linkages and hydraulic cylinders for moving the linkages as described in U.S. Pat. No. 4,679,803. In that mechanism, one set of links is provided forwardly and another set is provided rearwardly, and hydraulic cylinders connect the links both laterally and longitudinally to tilt the turntable relative to the carriage both about a lateral axis and a longitudinal axis. Other mechanisms for positioning and orienting the swing-house assembly relative to the carriage are also discussed in U.S. Pat. No. 4,679,803.
Another consideration in a forestry machine is machine height. This is important because these machines are oftentimes transported over the road. If the machine is too high in its shipping position, it will not make it under bridges or other underpasses, or may otherwise exceed the legal height limit of the road. Thus, the need for a leveling mechanism, which adds to the height of the machine, competes against providing a machine which can be transported over the road.